I would spend the money needed for game cams on improving the coop.
It doesn't matter what you see, especially if you see them kill your chickens.
Improve the coop and you won't have to worry about what might be out there.
Game Cameras are a GREAT tool for the poultry keeper....you can determine what is trying to get into your coop at night and find those "weak" spots in advance. It will tell you what you need to do regarding traps or fire-power!!! Coyotes and Fox are not as easy to trap as some would think and a 12 ga is good medicine if you dont mind sitting out in the dark a few times with a good light. Raccoons are the most common problem in my area and I have killed over 30 this summer and the game cameras helped me determine where they are coming from so I could set traps in the best locations!
Thats a great tip, I've got a couple, haven't used them for this yet. But I plan to if the need arises.. I play a radio on medium volume and have a bug zapper light on the side of the coop, the combination work great and I have plenty of predators, have killed many coyotes off my porch some less than 20 yards.